Preheat the oven to 350°F. Grease two 9-inch round cake pans, line the bottoms with parchment, and lightly flour the sides.

Whisk the flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large bowl. Add the eggs, buttermilk, oil, and vanilla, then whisk until smooth.

Slowly whisk in the hot coffee until the batter is glossy and quite thin. Divide the batter between the prepared pans.

Bake for 28 to 32 minutes, or until a toothpick inserted into the centers comes out with a few moist crumbs. Cool the cakes in their pans for 10 minutes, then transfer them to a rack to cool completely.

For the buttercream, beat the softened butter until creamy. Add the powdered sugar, cocoa powder, cream, vanilla, and salt, then mix on low until combined before beating on medium-high until fluffy.

Place one cooled cake layer on a serving plate and spread it with frosting. Add the second layer, cover the top and sides with the remaining buttercream, and garnish as desired.